nir: remove field only used in GLSL IR when assigning varying locations

This field is used as a flag to optimise out any varyings that don't have
a matching varying on the other side of the interface.

The value should be the same for all varyings (except for SSO but we can't
optimise those) by the time they reach nir and are no longer be needed.

Acked-by: Jason Ekstrand <jason.ekstrand@intel.com>

src/glsl/nir/glsl_to_nir.cpp

@@ -364,7 +364,6 @@ nir_visitor::visit(ir_variable *ir)
    var->data.explicit_index = ir->data.explicit_index;
    var->data.explicit_binding = ir->data.explicit_binding;
    var->data.has_initializer = ir->data.has_initializer;
-   var->data.is_unmatched_generic_inout = ir->data.is_unmatched_generic_inout;
    var->data.location_frac = ir->data.location_frac;
    var->data.from_named_ifc_block_array = ir->data.from_named_ifc_block_array;
    var->data.from_named_ifc_block_nonarray = ir->data.from_named_ifc_block_nonarray;

src/glsl/nir/nir.h

@@ -215,15 +215,6 @@ typedef struct {
        */
       unsigned has_initializer:1;
 
-      /**
-       * Is this variable a generic output or input that has not yet been matched
-       * up to a variable in another stage of the pipeline?
-       *
-       * This is used by the linker as scratch storage while assigning locations
-       * to generic inputs and outputs.
-       */
-      unsigned is_unmatched_generic_inout:1;
-
       /**
        * If non-zero, then this variable may be packed along with other variables
        * into a single varying slot, so this offset should be applied when